Transformers like that can get a pretty good hum going, tho these were probably well made to not be too noisey. The equipment always looks so archaic, but the sound was so good that they recorded, always amazes me.

Absolutely—hats off to the engineers for all that bouncing down and barely any noise at all (4 tracks on 2-inch tape helps). A masterly job. Though those Green Machine BRT things still look like something off the Flinstones.

In this case inches wide matters -as well as inches long (i.e. tape speed)- as it allows more resolution. When they recorded onto 1/4″ twin-track, the Beatles got 1/8″ per track. This was mixed to 1/4″ mono adding a bit of tape hiss but also gaining resolution (i.e. 1/8″ per track -> 1/4″ per track). If the song was mixed to 1/4″ stereo then resolution stayed equal but hiss was added. When recording onto 1 inch 4-track, each track got 1/4″. Hence, resolution was better to begin with, and degradation was at mixdown. In 1965, with reduction mixes, lots of hiss started being the norm, and that was when E.M.I. Hayes designed a noise reduction system similar to what would later be the Dolby system. Resolution degraded when migrating to 1 inch 8-track, as each track got 1/8″ tape. The less inches per track the more tape hiss too.